The present application claims priority under 35 U.S.C xc2xa7119 to Japanese Patent Application No.2000-13891, filed Jan. 18, 2000 entitled xe2x80x9cMETHOD OF DETERMINING RACEWAY SURFACE LENGTH AND ROLLING BODY DIAMETER OF MOTION ROLLING GUIDE DEVICE, AND MOTION ROLLING GUIDE DEVICE AND MOTION ROLLING GUIDE SYSTEM UTILIZING THE DETERMINING METHOD.xe2x80x9d The contents of that application are incorporated herein by reference in their entirety.
The present invention relates to a motion rolling guide device, and more particularly, to a method of determining a length of a raceway surface and a diameter of a rolling body of a motion rolling guide device, to a motion rolling guide device and to a motion rolling guide system utilizing such determining method.
There are known linear motion ball guide, ball bush, ball spline and the like as a motion rolling guide device for guiding a linear or curvilinear motion. In such motion rolling guide devices, the linear motion ball guide comprises a track shaft and a movable block as a movable member disposed to be movable with respect to the track shaft through a number of balls as rolling bodies. A linear motion ball guide system as a motion rolling guide system is a system in which the linear motion guide device is assembled with a table of a machine tool or the like and, for example, two movable blocks are assembled to two track shafts respectively for supporting the table with total four movable blocks.
In such system the table is applied a radial load, horizontal load, and respective moment loads of rolling load, yawing load and pitching load as external forces. The table changes its posture by virtue of these external forces, and the table posture includes five variable components of vertical (perpendicular) displacement, horizontal (transverse) displacement, rolling angle, yawing angle and pitching angle.
The movable block has a raceway surface, and a number of balls are disposed between this raceway surface and a track rail as a track shaft. In the linear motion ball guide, balls roll in accordance with the movement of the movable member and, therefore, a relative position of the balls and the movable block is variable. This variation of the relative position of the balls and the movable block causes a change of load distribution in the linear motion guide system, and hence, the posture of the table varies. The variable amount of the posture of the table represents the precision of the linear motion ball guide system, and accordingly, by lowering this variable amount of the table posture, the precision of the linear motion ball guide system can be improved.
In view of the circumstances in the prior art mentioned above, an object of the present invention is to provide a method of determining a length of a raceway surface of a movable member and a diameter of a rolling body of a rolling guide device, and a rolling guide device and a rolling guide system utilizing such determining method, which can reduce or lower the variable five components of an posture of a member to be moved, which represent a precision of a motion rolling guide system, particularly, in consideration of variable load distribution in accordance with the variation of the relative position of a movable member and a number of rolling bodies.
In the motion rolling guide device, the relative positions of the respective rolling bodies and the movable member are variable in accordance with the stroke, and when the stroke reaches to 2 xcexa Da (rolling body pitch or retainer pitch), one cycle is completed and, thereafter, this cycle is repeated. In the interval of this 2 xcexa Da stroke, since the relative positions of the rolling bodies vary, the load distribution in the motion rolling guide device varies and, hence, the posture of a table of the motion rolling guide system varies in accordance with the variation of this load distribution.
The inventors of the subject application analyzed the precision of a linear motion ball guide system by dividing the 2 xcexa Da stroke of the movable member and solving equations of equilibrium concerning the external loads and rolling body loads at respective positions to thereby obtain five variable components of the posture of the table. In such analysis, the deformation of a flange portion of the movable member has been considered to make it possible to analyze the precision in more actual manner.
According to the result of such analysis, it was found that as the diameter of the rolling body decreases, the radial displacement, the pitching and the maximum distribution load become smaller, but the radial displacement and the pitching angle variation representing the precision of the motion rolling guide system is not simply proportional to the diameter of the rolling body. That is, it was found that there exists any factor other than the diameter of the rolling body which gives an influence to such precision. As this factor, the inventors had paid their attentions to a ratio of the variation of the number of effective rolling bodies contributing the load in the 2 xcexa Da stroke and had found out that the variations of the radial displacement and pitching angle could be made extremely small by making this ratio a certain value to thereby remarkably enhance the precision of the linear motion guide system.
In consideration of the above matters, the objects of the present invention can be achieved by providing, in one aspect, a method of determining a raceway surface length of a movable member and a diameter of a rolling body of a motion rolling guide device which comprises a movable member and rolling bodies, wherein, in a stroke of 2 xcexa Da of the movable member at which relative positions of the movable member and the respective rolling bodies vary, a ratio (I:Ixe2x88x921) of a range in which the number of effective rolling bodies is I and a range in which the number of effective rolling bodies is Ixe2x88x921 is about 100% to 0% (100%:0%), wherein I=int(2Ux/xcexa Da+0.5), 2Ux: length of raceway surface of movable member and xcexa Da: rolling body pitch or retainer pitch.
According to the invention of this aspect, the change of the number of effective rolling bodies due to the stroke is reduced and the precision of the motion rolling guide system, particularly the pitching precision, can be remarkably improved. Moreover, when the change of the number of effective rolling bodies is reduced, influence given to the pitching precision by changing the diameter of the rolling body is also reduced, and for example, the diameter of the rolling body can be made large while maintaining the pitching precision, and the basic dynamic load rating can be also made large.
The above object can be also achieved by providing, in a further aspect, a motion rolling guide device comprising a movable member and rolling bodies, wherein a length of a raceway surface of the movable member and a diameter of the rolling body are determined such that, in a stroke of 2 xcexa Da of the movable member at which relative positions of the movable member and the respective rolling bodies vary, a ratio (I:Ixe2x88x921) of a range in which the number of effective rolling bodies is I and a range in which the number of effective rolling bodies is Ixe2x88x921 is about 100% to 0% (100%:0%), wherein I=int(2Ux/xcexa Da+0.5), 2Ux: length of raceway surface of movable member and xcexa Da: rolling body pitch or retainer pitch.
The above object can be also achieved by providing, in a still further aspect, a motion rolling guide system comprising a track rail, at least one movable member mounted to the track rail to be movable and rolling bodies disposed between the track rail and the movable member, wherein a length of a raceway surface of the movable member and a diameter of the rolling body are determined such that, in a stroke of 2 xcexa Da of the movable member at which relative positions of the movable member and the respective rolling bodies vary, a ratio (I:Ixe2x88x921) of a range in which the number of effective rolling bodies is I and a range in which the number of effective rolling bodies is Ixe2x88x921 is about 100% to 0% (100%/: 0%), wherein I=int(2Ux/xcexa Da+0.5), 2Ux: length of raceway surface of movable member and xcexa Da: rolling body pitch or retainer pitch.
Furthermore, the inventors had also paid their attentions, as another factor, to the relative positions of the rolling bodies in the movable members disposed at forward and rearward positions in the same track shaft of the linear motion guide system and found out that the variation of the pitching angles can be remarkably reduced by adjusting the spans of the movable members so as to make the relative positions of the rolling bodies coincident with each other.
That is, the above object can be achieved according to the present invention by providing, in a still further aspect, a motion rolling guide system comprising a track means, a plurality of movable members mounted to the track means and number of rolling bodies disposed between the track means and the movable members, wherein spans of the movable members are adjusted so that relative positions of the rolling bodies in the respective movable members accord with each other. This adjustment is realized by making the span of the movable member integral multiples of the rolling body pitch 2 xcexa Da.
In a structure in which the guide system is provided with a plurality of track shafts, the span of the movable member may be adjusted so that the relative positions of the rolling bodies in the movable members mounted to the respective track shafts accord with each other.
Still furthermore, the present invention can provide the combination of the above two factors (aspects), that is, there is provided a motion rolling guide system, in which a plurality of movable members are mounted to the track means, wherein a length of a raceway surface of the movable member and a diameter of the rolling body are determined such that, in a stroke of 2 xcexa Da of the movable member at which relative positions of the movable member and the respective rolling bodies vary, a ratio (I:Ixe2x88x921) of a range in which the number of effective rolling bodies is I and a range in which the number of effective rolling bodies is Ixe2x88x921 is about 100% to 0% (100%:0%), wherein I=int(2Ux/xcexa Da+0.5), 2Ux: length of raceway surface of movable member and xcexa Da: rolling body pitch or retainer pitch.
According to such aspect, the above two effects or functions can be effectively combined and the precision of the motion rolling guide system can be further enhanced.
Still furthermore, the present invention can provide the combination of the above two factors (aspects), that is, there is provided a motion rolling guide system, in which a plurality of movable members are mounted to the track means, wherein a length of a raceway surface of the movable member and a diameter of the rolling body are determined such that, in a stroke of 2 xcexa Da of the movable member at which relative positions of the movable member and the respective rolling members vary, a ratio (I:Ixe2x88x921) of a range in which the number of effective rolling bodies is I and a range in which the number of effective rolling bodies is Ixe2x88x921 is about 50% to 50% (50%:50%), wherein I=int(2Ux/xcexa Da+0.5), 2Ux: length of raceway surface of movable member and xcexa Da: rolling body pitch or retainer pitch.
According to such aspect, the above two effects or functions can be also effectively combined and the precision of the motion rolling guide system can be further enhanced.
The further characteristic features of the present invention will be made more clear from the descriptions made with reference to the accompanying drawings.